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Re: [lwip-users] Sending too slow.

From: Kieran Mansley
Subject: Re: [lwip-users] Sending too slow.
Date: Wed, 13 Sep 2006 10:58:34 +0100

On Wed, 2006-09-13 at 09:09 +0100, Bob Grice wrote:
> Hi Mateusz ,
> The way that the packets are being sent (1460 followed by 40) is because
> of an issue in tcp_enqueue that I noticed last November, unfortunately I
> haven't had time to submit what would be a quite complicated patch..
> The problem is benign apart from the fact it makes the link inefficient.
> Tcp_enqueue first splits the received data into segments all of mss size
> apart from the last, it then checks the last segment on the unsent queue
> and attempts to join the segments if the last is also less then mss.
> This works fine if you are doing small writes, however if you do writes
> (worst case mss+1 bytes) you end up with <mss> <1 byte> <mss> <1 byte>
> rather than <mss> <mss> <2 bytes>.
> Basically, the code needs modifying to check the space of the last
> unsent before it splits the new data into mss sized units, but this
> would need quite a large patch...

Thanks for the explanation - I think that while this would be nice, it's
not worth going to a lot of effort.  

> I don't know if either of these changes made it into the current
> surface, as I haven't been working with lwip for the last year or so,
> but hopefully it will give you something to look at.

I think it hasn't.  Did you file a bug/patch on savannah when mentioning
it before?  If not, and you have the time, it would be a great help if
you could do so.



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